The Copahue volcano, which sits in the Andes cordillera, straddling the border with Argentina's Neuquen province, started spewing ash and gas on Saturday.

Officials issued a yellow and orange alert at first, but on Sunday Chile's emergency office ONEMI raised that in the Biobio region after it registered seismic activity on Saturday night and a cloud of ash billowed almost a mile high.

"Authorities have overflown the volcano area and the alert is still red," Gilda Grandon of ONEMI's BioBio unit said. "We have noted some drop in the ash plume but the alert level is maintained because a full eruption is not ruled out."

The Mining Ministry's Sernageomin geology unit has recommended careful observation of a nine-mile radius around the active crater in case of mudflows of volcanic fragments. Officials say there is no need yet to evacuate.

The 9,833ft Copahue erupted in 1991. The volcano became highly active with blasts and gases in 2001 in its worst activity in more than 20 years.

A volcano in the Caulle Cordon of southern Chile erupted violently last year, forcing the cancellation of hundreds of flights and the evacuation of more than 3,500 people.